With less than a month remaining before the Berkshire Museum begins its planned sale of 40 artworks from its collection, a group that includes family members of the artist Norman Rockwell has filed a complaint and motion in state court seeking to block the sale.

“The Berkshire Museum’s planned deaccession violates the museum’s establishing statute, promises made to donors and the fiduciary obligations of its trustees,” attorney Michael B. Keating, who represents the plaintiffs, said in a statement. “This move is also antithetical to the museum’s stated charitable purpose, and is financially unnecessary.”

The Berkshire Museum announced last July that it intended to sell the artworks to strengthen its endowment and fund renovations as part of a shift toward science and history. The 40 artworks — which include two paintings by Rockwell — are set to be sold in a series of auctions beginning Nov. 13, through Sotheby’s, which estimates they could fetch more than $68 million.

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The Pittsfield museum has come under intense criticism since announcing the sale. The Massachusetts Cultural Council, the American Alliance of Museums, and the Association of Art Museum Directors have all denounced the plan, which is under review by the Massachusetts attorney general’s office.

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“There’s irreparable harm if the art is sold: it will never be available to people in Berkshire County — and maybe the US — again,” said Keating. “We’re asking for the court to enter a temporary restraining order so the sale would not go through. That would give the court and the attorney general’s office time to review our contention and figure out whether the sale can legally be affected.”

William F. Lee, an attorney who represents the museum, said the museum was on solid legal footing.

“We are confident that the Museum has the right to go forward and that the lawsuit is factually and legally flawed,” he said in a statement. “We will respond to the claims in court.”

In the complaint filed Friday, which also names Massachusetts attorney general Maura Healey “as a necessary party,” the plaintiffs argue that the sale “violates the Museum’s establishing statute and promises made to donors.” It argues that Rockwell, who originally donated the two paintings to the museum, did so “with the intent that they be permanently displayed to the public in Pittsfield, and on the understanding that the Museum would do so pursuant to its mandate.”

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“By planning and approving the sale described herein,” the plaintiffs argue, “the Museum [is] acting in breach of fiduciary duty, in breach of trust, and without legal authority.”

Berkshire Museum executive director Van Shields has described the sale as a matter of economic survival for the museum, which he said has an ongoing structural deficit of about $1.15 million.

The MCC has questioned the museum’s economic analysis, noting in a statement that “two independent analyses, along with our own review of the Museum’s audited financial statements, show clearly that the Museum could put itself in a healthy operating position without deaccessioning art.”

Elizabeth McGraw, president of the museum’s board of trustees, said in a statement that the sale would help ensure the museum’s continued existence.

“We believe we have strong legal grounds for our deaccessioning, and we are confident in our New Vision plan which will allow this important local museum to continue to contribute to the educational and cultural life of this region for another century.”